Carbon nanotube electron gun

ABSTRACT

An electron gun, an electron source for an electron gun, an extractor for an electron gun, and a respective method for producing the electron gun, the electron source and the extractor are disclosed. Embodiments provide an electron source utilizing a carbon nanotube (CNT) bonded to a substrate for increased stability, reliability, and durability. An extractor with an aperture in a conductive material is used to extract electrons from the electron source, where the aperture may substantially align with the CNT of the electron source when the extractor and electron source are mated to form the electron gun. The electron source and extractor may have alignment features for aligning the electron source and the extractor, thereby bringing the aperture and CNT into substantial alignment when assembled. The alignment features may provide and maintain this alignment during operation to improve the field emission characteristics and overall system stability of the electron gun.

RELATED APPLICATIONS

The present application is related to and claims the benefit of U.S.Provisional Patent Application No. 60/921,134, filed Mar. 30, 2007,entitled “CARBON NANOTUBE ELECTRON GUN,” naming Cattien V. Nguyen andBryan P. Ribaya as inventors, assigned to the assignee of the presentinvention, and having attorney docket number NASA-P1002.PRO. Thatapplication is incorporated herein by reference in its entirety and forall purposes.

The present application is related to U.S. patent application Ser. No.11/729,124, filed Mar. 27, 2007, entitled “CARBON NANOTUBE ELECTRONSOURCE,” naming Cattien V. Nguyen as the inventor, assigned to theassignee of the present invention, and having attorney docket numberNASA-P1001. That application is incorporated herein by reference in itsentirety and for all purposes.

GOVERNMENT INTERESTS

The invention described herein was made by non-government employees,whose contributions were made in the performance of work under a NASAcontract, and is subject to the provisions of Public Law 96-517 (35U.S.C. §202). This invention was made with Government support undercontract NAS2-03144 awarded by NASA. The Government has certain rightsin this invention.

BACKGROUND OF THE INVENTION

A carbon nanotube (CNT) is one or more sheets of graphite rolled into atube with a diameter on the order of a nanometer. Single-walled carbonnanotubes (SWNTs) consist of a single sheet of graphite with a thicknessof roughly one atom, whereas multi-walled carbon nanotubes (MWNTs)consist of multiple sheets of graphite rolled into concentric tubes. Ingeneral, CNTs are an attractive option for electron emission given theirrobust physical, chemical and electrical properties. And in particular,CNTs perform well as cold field emitters due to their high aspect ratiosproviding low turn-on fields.

Given the robust properties of CNTs and their ability to emit electrons,CNTs can make very effective electron sources for electron fieldemission guns. However, the performance of the electron gun is dependentupon the implementation of the CNT within the electron gun, as well asthe overall configuration of the electron gun itself. Most conventionalelectron guns utilize poor CNT implementation and electron gunconfiguration, and as such, exhibit poor field emission characteristics,stability, reliability, and durability.

For example, U.S. Pat. No. 7,151,268 to Fujieda et al. discusses aconventional electron gun using a conventional extractor to extractelectrons from an electron source. The electron gun discussed in the'268 patent has no provision for aligning the CNT with the extractor,thereby requiring complex and expensive focusing electron optics.Additionally, the misalignment of the extractor and the CNT inconventional electron guns requires the use of large focusing electronoptics. Accordingly, conventional electron guns cannot be used in manyminiaturized applications.

SUMMARY OF THE INVENTION

Accordingly, a need exists to provide an improved electron source foruse in electron guns. A need also exists for an improved extractor foruse in electron guns. Additionally, a need exists to provide an electrongun with improved alignment of the carbon nanotube and extractor.Embodiments of the present invention provide novel solutions to theseneeds and others as described below.

Embodiments of the present invention are directed to an electron gun, anelectron source for an electron gun, an extractor for an electron gun,and a respective method for producing the electron gun, the electronsource and the extractor. More specifically, embodiments provide anelectron source utilizing a carbon nanotube (CNT) bonded to a substratefor increased mechanical and electrical stability, reliability, anddurability. An extractor with an aperture in a conductive material isused to extract electrons from the electron source, where the aperturemay substantially align with the CNT of the electron source when theextractor and electron source are mated to form the electron gun. Theelectron source and extractor may have alignment features for aligningthe electron source and the extractor, thereby bringing the aperture andCNT into substantial alignment when assembled. The alignment featuresmay provide and maintain this alignment during operation to improve thefield emission characteristics and overall system stability of theelectron gun.

In one embodiment, an electron source includes a substrate and aconductive material disposed on the substrate. The electron source alsoincludes a carbon nanotube coupled to the conductive material. Thesubstrate may include a feature for accepting the carbon nanotube, andwherein the carbon nanotube is coupled to a portion of the conductivematerial disposed on the feature. The substrate may also include atleast one alignment feature for aligning the carbon nanotube with anextractor aperture of the electron gun.

In another embodiment, a method of producing an electron source includesetching a substrate to create a feature for accepting a carbon nanotube.A conductive material is applied to the substrate. The carbon nanotubemay be coupled to a portion of the conductive material disposed on thefeature. The coupling may include applying an electric potential betweenthe carbon nanotube and the conductive material, and also welding thecarbon nanotube to the portion of the conductive material disposed onthe feature. The method may also include adjusting a length of thecarbon nanotube using joule heating, where the adjusting includesinducing stress in a region of the carbon nanotube to increase anelectrical resistance of the region. A current is passed through thecarbon nanotube to induce joule heating at the region. The current isadjusted until the joule heating causes the carbon nanotube to break atthe region.

In yet another embodiment, an electron gun includes an electron sourceincluding a carbon nanotube and a first conductive material electricallycoupled to the carbon nanotube, wherein the electron source is operableto emit electrons in response to an application of an electric potentialto at least one of the carbon nanotube and the first conductivematerial. The electron gun also includes an extractor including a secondconductive material with an aperture, wherein the extractor is operableto at least one of extract and accelerate electrons emitted from theelectron source in response to the application of the electric potentialbetween the second conductive material and at least one of the carbonnanotube and the first conductive material. The electron source includesa first alignment feature and the extractor includes a second alignmentfeature, and wherein the first and second alignment features are forsubstantially aligning the carbon nanotube with the aperture. The firstand second alignment features may be operable to interface with oneanother when the extractor is mated with the electron source.

In another embodiment, an array of electron guns includes a firstelectron gun including a first electron source including a first carbonnanotube, wherein the first electron source is operable to emitelectrons in response to an application of an electric potential to thecarbon nanotube. A first extractor includes a first conductive materialwith a first aperture for at least one of extracting and acceleratingelectrons emitted from the electron source in response to theapplication of the electric potential between the first conductivematerial and the first carbon nanotube. The first electron source andthe first extractor each comprise at least one alignment feature forsubstantially aligning the first carbon nanotube with the firstaperture. The array of electron guns also includes a second electron gunlocated in proximity to the first electron gun, where the secondelectron gun includes a second electron source comprising a secondcarbon nanotube, wherein the second electron source is operable to emitelectrons in response to an application of an electric potential to thecarbon nanotube. A second extractor includes a second conductivematerial with a second aperture for at least one of extracting andaccelerating electrons emitted from the electron source in response tothe application of the electric potential between the second conductivematerial and the second carbon nanotube. The second electron source andthe second extractor may each comprise at least one alignment featurefor substantially aligning the second carbon nanotube with the secondaperture.

In yet another embodiment, a method of producing an extractor for anelectron gun includes identifying a reference point common to both anelectron source and an extractor when the extractor is mated with theelectron source. A relative position of a carbon nanotube of saidelectron source is determined with respect to the reference point. Anaperture is then created in a conductive material of the extractor atthe relative position with respect to the reference point, wherein theaperture is substantially aligned with the carbon nanotube when theextractor is mated with the electron source. The electron source and theextractor may each comprise at least one alignment feature formaintaining alignment of the electron source and the extractor whenmated, and wherein the reference point is associated with the alignmentfeature. The creating the aperture may include focused ion beam millingthe conductive material of the extractor to generate the aperture.Additionally, the method may include fabricating the extractor, wherethe fabricating may include disposing the conductive material on asubstrate and etching the substrate to create at least one alignmentfeature for aligning the extractor with the electron source.

In another embodiment, a method of providing field emission currentusing an electron gun includes applying an electric potential between anelectron source and an extractor of the electron gun, wherein theelectron source and the extractor each comprise at least one respectivealignment feature for substantially aligning a carbon nanotube of theelectron source with an aperture of the extractor. The method alsoincludes extracting electrons from the carbon nanotube using theextractor to provide the field emission current. The method may alsoinclude using the field emission current to perform at least one ofelectron microscopy, electron-beam metrology, and electron-beamlithography.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements.

FIG. 1 shows an exemplary process for producing an electron source inaccordance with one embodiment of the present invention.

FIG. 2A shows a first set of exemplary production stages of an electronsource in accordance with one embodiment of the present invention.

FIG. 2B shows a second set of exemplary production stages of an electronsource in accordance with one embodiment of the present invention.

FIG. 3 shows an exemplary setup for coupling a carbon nanotube to asubstrate of an exemplary electron source in accordance with oneembodiment of the present invention.

FIG. 4 shows an exemplary process for adjusting the length of a carbonnanotube in accordance with one embodiment of the present invention.

FIG. 5 shows an exemplary process for producing an extractor for anelectron gun in accordance with one embodiment of the present invention.

FIG. 6A shows a set of exemplary production stages of an electron gunextractor with a non-uniform substrate in accordance with one embodimentof the present invention.

FIG. 6B shows a set of exemplary production stages of an electron gunextractor with a uniform substrate in accordance with one embodiment ofthe present invention.

FIG. 7 shows an assembled view of an exemplary electron gun prior tocreating an aperture in the extractor in accordance with one embodimentof the present invention.

FIG. 8 shows an assembled view of an exemplary electron gun with anaperture in the extractor in accordance with one embodiment of thepresent invention.

FIG. 9 shows an exemplary array of electron guns in accordance with oneembodiment of the present invention.

FIG. 10 shows an exemplary process for providing field emission currentusing an electron gun in accordance with one embodiment of the presentinvention.

FIG. 11 shows exemplary field emission from an exemplary electron gun inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. While the present invention will be discussed in conjunctionwith the following embodiments, it will be understood that they are notintended to limit the present invention to these embodiments alone. Onthe contrary, the present invention is intended to cover alternatives,modifications, and equivalents which may be included with the spirit andscope of the present invention as defined by the appended claims.Furthermore, in the following detailed description of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, embodiments ofthe present invention may be practiced without these specific details.In other instances, well-known methods, procedures, components, andcircuits have not been described in detail so as not to unnecessarilyobscure aspects of the present invention.

EMBODIMENTS OF THE INVENTION

FIG. 1 shows exemplary process 100 for producing an electron source,commonly referred to as a cathode, in accordance with one embodiment ofthe present invention. FIGS. 2A and 2B show sets 200A and 200B ofexemplary production stages of an electron source (e.g., amicro-electro-mechanical-system (MEMS) based electron source) inaccordance with one embodiment of the present invention. In oneembodiment, the production stages depicted in Figures 2A and 2B maycorrespond with one or more steps of process 100. As such, FIGS. 2A and2B will be described in conjunction with FIG. 1.

As shown in FIG. 1, step 110 involves etching a substrate to create afeature for accepting a carbon nanotube. For example, as shown in FIG.2A, substrate 210 may be etched to form feature 220. Substrate 210 maycomprise a non-conductive material in one embodiment. Alternatively,substrate 210 may comprise a semi-conductive material, such as silicon(e.g., using a silicon <100> wafer), in another embodiment.Additionally, feature 220 may be formed by appropriately maskingsubstrate 210 and applying an etching process (e.g., a reactive ion etch(RIE)) to etch the unmasked portions.

Feature 220 may be shaped to enable attachment of a carbon nanotube(CNT), and also to provide adequate mechanical and electrical stabilityfor the CNT during operation. Additionally, the dimensions (e.g.,length, width, diameter, etc.) of feature 220 may be varied to controlemission properties of the CNT. For example, in one embodiment, the sizeof feature 220 may be increased to increase the turn-on voltage of theCNT, thereby decreasing the electric field at the CNT tip. And in oneembodiment, feature 220 may comprise a post having a height and diameterof approximately 70 μm.

As shown in FIG. 1, step 120 involves adding an alignment feature to thesubstrate for aligning an extractor to the completed electron source.For example, substrate 210 may be further etched in one embodiment tocreate alignment feature 230 for aligning the electron source to anextractor of an electron gun. The extractor, or any components disposedbetween the electron source and the extractor in the assembled electrongun, may comprise one or more features for interfacing with feature 230of the electron source. As such, the electron source may align with theextractor when the electron gun is assembled, thereby substantiallyaligning the CNT of the electron source with an aperture of theextractor in one embodiment. Thus, the electron gun utilizing theelectron source produced in FIGS. 2A and 2B may exhibit improved fieldemission characteristics, stability, reliability, and durability.

Alignment feature 230 may be formed by appropriately masking substrate210 and applying an etching solution to etch the unmasked portions. Inone embodiment, alignment feature 230 may be formed in accordance withMEMS fabrication technology. The mask applied to substrate 210 may bebased upon alignment features of an existing extractor such that feature230 may appropriately mate with one or more of the alignment features ofthe extractor after etching. Where substrate 210 comprises silicon(e.g., using a silicon <100> wafer), a KOH wet etch solution (e.g., alsocomprising water and isopropyl alcohol) may be applied to substrate 210to form surfaces 232 and 234 of feature 230. Surfaces 232 and 234 mayhave substantially equal angles (e.g., with respect to base 240 ofsubstrate 210), where the angles may be a result oforientation-dependent etching of substrate 210. In one embodiment,surfaces 232 and 234 may represent 111-planes at approximately 54.7degrees from the 100-plane. Additionally, in one embodiment, the etchingof substrate 210 may produce upper surface 236 with dimensions ofapproximately 170 μm by 170 μm and bottom surface 238 with dimensions ofapproximately 300 μm by 300 μm.

Alternatively, alignment feature 230 may comprise a separate objectadded to substrate 210. For example, feature 230 may comprise any object(e.g., a block, post, etc.) coupled (e.g., bonded, press-fit, etc.) tothe substrate for interfacing with a feature (e.g., edge, surface,object coupled to, etc.) of an extractor or any other object disposedbetween the electron source and the extractor in the assembled electrongun. And in other embodiments, feature 230 may comprise a portionremoved from substrate 210 (e.g., to create a hole, etc.), where theremoved portion may interface with a feature of the extractor orinterfacing object, may enable use of a tool for aligning the electronsource and extractor, etc.

As shown in FIG. 1, step 130 involves applying a conductive material tothe substrate. For example, conductive material 250 may be applied tofeature 220, feature 230, and base 240 as shown in FIG. 2B. Theconductive material may comprise a material operable to bond to thesubstrate material. In one embodiment, where the substrate comprisessilicon, conductive material 250 may comprise nickel or another metaloperable to form a strong interface with a CNT. Additionally,application of conductive material 250 to feature 230 may createsurfaces 232 a and 234 a which are substantially parallel to respectivesurfaces 232 and 234 as depicted in FIG. 2A.

Although conductive material 250 is depicted in FIG. 2B to cover almostall of feature 220, feature 230 and base 240, it should be appreciatedthat conductive material 250 may only cover select regions of thesubstrate in other embodiments. For example, in one embodiment, material250 may form a pad (e.g., on feature 220) and an electrode (e.g.,disposed on feature 220, feature 230, base 240, or a combination thereofcoupled to the pad for applying an electric potential to the CNT (e.g.,to provide field emission current). Additionally, although conductivematerial 250 is depicted with a consistent thickness in FIG. 2B, itshould be appreciated that the thickness of material 250 may vary inother embodiments. Further, it should be appreciated that the elementsdepicted in FIGS. 2A and 2B may comprise different shapes, sizes, etc.in other embodiments.

As shown in FIG. 1, step 140 involves coupling a CNT to a portion of theconductive material disposed on the substrate. For example, CNT 260 amay be coupled to feature 220 and/or a portion of conductive material250 disposed on feature 220 as shown in FIG. 2B. The CNT (e.g., 260 a)may be coupled in a substantially perpendicular orientation with respectto base 240. Additionally, CNT 260 a may be chosen based upon one ormore physical characteristics (e.g., length, diameter, etc.) to vary orcontrol field emission characteristics (e.g., field enhancement, energyspread, brightness, stability, lifetime, etc.) of the electron source(e.g., produced as a result of process 100) and/or electron gunutilizing the electron source.

The CNT (e.g., 260 a) may be coupled by welding the CNT to conductivematerial (e.g., 250) disposed on the electron source substrate (e.g.,210). In one embodiment, joule heating may be used. For example, asshown in FIG. 3, CNT 260 a may be welded to conductive material 250 byapplying electric potential 310 to CNT 260 a (e.g., the tip of CNT 260a) and conductive material 250 (e.g., forming an electrode coupled toCNT 260 a). Alternatively, electric potential 310 may be applied betweenCNT 260 a (e.g., the tip of CNT 260 a) and the electron source substrate(e.g., feature 220, feature 230, base 240, etc.) as indicated by thedashed lines. Sufficient heat may be generated by the electricalresistance between the CNT (e.g., 260 a) and the conductive material(e.g., 250) to bond the CNT and the conductive material. In otherembodiments, other forms of welding and/or bonding may be used to coupleCNT to feature 220 and/or conductive material 250 disposed thereon.

Step 150 involves adjusting the length of the CNT. For example, as shownin FIG. 2B, CNT 260 a may be shortened to form CNT 260 b. The length ofthe CNT may be adjusted by cutting, shearing, breaking, joule heating(e.g., in accordance with process 400 of FIG. 4), etc. Additionally, anylength-adjusting procedure used to adjust the length of the CNT (e.g.,260 a, 260 b, etc.) may be repeated to further adjust the length. Assuch, completed electron source 270 may be produced upon adjusting theCNT (e.g., 260 a) to a predetermined length (e.g., as represented by CNT260 b). In one embodiment, CNT 260 b may have a length of approximately3 μm. It should be appreciated that step 150 may be optional where theCNT (e.g., 260 a) is of a desired length upon coupling it to thesubstrate (e.g., feature 220) and/or conductive material (e.g., 250)disposed thereon.

FIG. 4 shows exemplary process 400 for adjusting the length of a carbonnanotube in accordance with one embodiment of the present invention. Asshown in FIG. 4, step 410 involves inducing stress in a region of a CNTto increase the electrical resistance of the region. For example, CNT260 a of FIG. 2B may be bent, twisted, or otherwise strained to inducestress in a select region of the CNT. The region may be located at apoint along the CNT to which the CNT is to be shortened. As such, theelectrical resistance of the region may be increased given the stressesinduced in that region.

Step 420 involves passing a current through the CNT to induce jouleheating at the region. The current may be passed through the CNT byapplying an electric potential across the CNT, or between a tip of theCNT and an electrode coupled to the CNT. In one embodiment, the regionin which stress was induced in step 410 may produce more heat thansurrounding regions of the CNT (e.g., 260 a) given the relatively higherresistance of the region with respect to the surrounding regions (e.g.,in which stresses were not induced). An inert and conductive material(e.g., gold) may be used to contact the CNT and pass the current,thereby reducing the bonding between the CNT and the material during theheating.

As shown in FIG. 4, step 430 involves adjusting (e.g., increasing)and/or maintaining the current until the joule heating causes the CNT tobreak at the region. The region (e.g., that in which stress was inducedin step 410) may heat to a point such that the CNT (e.g., 260 a)degrades at the region, thereby causing the CNT to break and form ashortened CNT (e.g., 260 b). In one embodiment, the break at the regionmay produce a shortened CNT (e.g., 260 b) with a sharp (e.g., pointed,convex, etc.) emitter tip. Additionally, although the CNT may beshortened in step 430, the CNT may still maintain a high aspect ratio(e.g., length to diameter) in one embodiment. Further, in oneembodiment, process 400 may produce a CNT (e.g., 260 b) with a lengthresolution of +/−500 nm.

As such, embodiments provide convenient and effective means for varyingcharacteristics of the CNT (e.g., length, diameter, tube aspect ratio,etc.) to control field emission characteristics (e.g., fieldenhancement, energy spread, brightness, stability, lifetime, etc.) ofthe electron source and/or electron gun utilizing the electron source.Additionally, varying the CNT properties may also adjust the geometry orother characteristics of the electron gun utilizing the electron source,thereby enabling further control over field emission characteristics.For example, the length of the CNT may be used to control the distancebetween the CNT tip and the extractor in an assembled electron gun,where a longer CNT may equate to a shorter distance between the CNT tipand the extractor.

FIG. 5 shows exemplary process 500 for producing an extractor for anelectron gun in accordance with one embodiment of the present invention.As shown in FIG. 5, step 510 involves fabricating or receiving anextractor. An extractor received in step 510 may be pre-fabricated,either for use in electron guns or other applications. Alternatively, anextractor comprising a non-uniform substrate (e.g., as shown in FIG. 6Abelow) or a uniform substrate (e.g., as shown in FIG. 6B below) may befabricated or received in step 510.

Turning briefly to FIGS. 6A and 6B, FIG. 6A shows set 600A of exemplaryproduction stages of an electron gun extractor with a non-uniformsubstrate in accordance with one embodiment of the present invention,whereas FIG. 6B shows set 600B of exemplary production stages of anelectron gun extractor with a uniform substrate in accordance with oneembodiment of the present invention. As shown in FIG. 6A, non-uniformsubstrate 610 comprises membrane 630 disposed on substrate material 620.In one embodiment, substrate material 620 may comprise silicon. Inanother embodiment, substrate material 620 may comprise a metal (e.g.,where an insulating structure is used to substantially insulate theextractor from the electron source). Membrane 630 may comprise Si₃N₄,which may have a thickness of 200 nm in one embodiment.

Conductive material 640 may be disposed on membrane 630, where material640 may comprise metal in one embodiment. Material 640 may form anextractor electrode for applying an electric potential (e.g., which mayalso be applied to a CNT electrode), where the electric potential may beused to provide field emission current from an electron gun utilizingextractor 660.

As shown in FIG. 6A, feature 650 may be created in substrate material620. Feature 650 may comprise a recess for accepting one or moreportions of an electron source (e.g., CNT 260 b, feature 220 and feature230 of FIG. 2B), where surfaces 652 and 654 may form locating featuresfor interfacing with features (e.g., surfaces 232, 234, 232 a, 234 a,etc.) of the electron source (e.g., 270) and/or features of an objectdisposed between the electron source (e.g., 270) and the extractor(e.g., 660). As such, surfaces 652 and 654 may align or locate extractor660 with respect to an electron source (e.g., 270) when they are mated(e.g., coupled directly, coupled with one or more other componentscoupled between portions of the extractor and electron source, etc.).

In one embodiment, an angular relationship between surfaces 652 and 654may be substantially equal to an angular relationship between alignmentfeatures (e.g., surfaces 232, 234, 232 a, 234 a, etc.) of a matingelectron source. The angular relationship may be created by using asimilar substrate material for both the electron source alignmentfeatures (e.g., surfaces 232, 234, 232 a, 234 a, etc.) and the extractoralignment features (e.g., surfaces 652, 654, etc.), where the substratematerial (e.g., 620) comprises a material (e.g., silicon <100>) that isamenable to an orientation-dependent etch (e.g., using a mixture of KOH,water and isopropyl alcohol). Additionally, membrane 630 may besubstantially resistant to the etching in one embodiment, therebyforming a barrier between the substrate to be etched (e.g., substratematerial 620) and the conductive material (e.g., 640) disposed onmembrane 630. In other embodiments, other methods (e.g.,non-orientation-dependent etching, focused ion beam milling, etc.) maybe used to produce a similar angular relationship between alignmentfeatures of the electron gun and the extractor.

As shown in FIG. 6B, uniform substrate 670 comprises substrate material620. Conductive material 640 may be disposed directly on substratematerial 620 in one embodiment. Additionally, similar to the discussionwith respect to FIG. 6A, feature 650 may be formed in substrate material620, where feature 650 may accept one or more portions of an electronsource (e.g., CNT 260 b, feature 220 and feature 230 of FIG. 2B) matedwith extractor 690, form alignment features (e.g., surfaces 652 and/or654) for aligning an electron source to extractor 690, etc.

Although FIGS. 6A and 6B depict feature 650 with specific shapes, itshould be appreciated that the features (e.g., 650) may be alternativelyshaped in other embodiments. Additionally, although surfaces (e.g., 652,654, etc.) of the features are described as locating or alignmentfeatures, it should be appreciated that extractor 660 and/or 690 maycomprise alternative or additional alignment features in otherembodiments. Further, it should be appreciated that the alternativeand/or additional alignment features may be formed by adding to and/orremoving material from the extractors (e.g., 660 and/or 690).

Referring back to FIG. 5, step 520 involves identifying a referencepoint common to both an electron source and the extractor when theextractor is mated to the electron source. As shown in FIG. 7, assembledelectron gun 700 comprises extractor 660 mated to electron source 270,where the extractor and the electron source may share common referencepoint 710. The common reference point may be located at a point, line orsurface of the extractor (e.g., 660) and/or the electron source (e.g.,270) in one embodiment. Alternatively, a reference point may be commonto both the extractor and the electron source if the reference point isidentifiable with respect to both the extractor and the electron sourceindividually. For example, reference point 720 may be used as a commonreference point since it is identifiable with respect to extractor 660(e.g., a distance 730 away from surface 761 of extractor 660) and withrespect to electron source 270 (e.g., a distance 730 away from surface771 of electron source 270).

As shown in FIG. 5, step 530 involves determining a relative position ofa CNT of the electron source (e.g., 270) with respect to the referencepoint (e.g., determined in step 520). As shown in FIG. 7, relativeposition 740 of CNT 260 b (e.g., axis 750) may be determined withrespect to reference point 710. Alternatively, relative position 760 ofCNT 260 b (e.g., axis 750) may be determined with respect to referencepoint 720. In one embodiment, an electron microscope (e.g., a scanningelectron microscope) may be used to determine the relative position ofthe CNT (e.g., 260 b) with respect to the reference point (e.g., 710,720, etc.).

After a relative position is determined, an aperture may be created inthe conductive material of the extractor in step 540 at the relativeposition (e.g., determined in step 530) with respect to the referencepoint. For example, as shown in FIG. 8, aperture 810 may be createdalong axis 820 of electron gun 800, where axis 810 may be located at arelative position (e.g., 740, 760, etc.) with respect to a referencepoint (e.g., 710, 720, etc.). As such, in one embodiment, aperture 810may share an axis (e.g., 820) with CNT 260 b (e.g., 750).

Further, it should be appreciated that process 800 enables aperture 810to be substantially aligned with the CNT (e.g., 260 b) regardless of thelocation and/or orientation of the CNT mounting in the electron source(e.g., 270), thereby enabling the use of more lenient CNT alignmenttolerances when manufacturing the electron source. Thus, embodiments canreduce the cost and time associated with manufacturing the electronsources (e.g., 270) and/or electron guns (e.g., 800), as well asreducing the failure rate of the manufactured electron sources and/orelectron guns. Further, by improving the alignment of the CNT (e.g., 260b) with the extractor (e.g., extractor aperture 810), embodiments enablethe use of the smaller and less-expensive focusing electron optics. Andin other embodiments, focusing electron optics may not be required giventhe alignment of the CNT (e.g., 260 b) with the extractor aperture(e.g., 810)

Aperture 820 may be created in conductive material 640 and/or membrane630 by using focused ion beam milling in one embodiment. The aperturemay have a diameter ranging from approximately 20 nm to hundreds ofmicrons in one embodiment. Although aperture 810 is depicted in FIG. 8as a straight, round hole, it should be appreciated that aperture 810may be alternatively shaped in other embodiments.

Accordingly, embodiments provide convenient and effective mechanisms(e.g., surfaces 652/654 and surfaces 232 a/234 a) for aligning a CNT(e.g., 260 b) of an electron source (e.g., 270) with an extractoraperture (e.g., 810), thereby increasing the field emissioncharacteristics and overall system stability of the electron gun duringoperation. Additionally, the geometry or other characteristics of theelectron gun (e.g., by varying the length of CNT 260 b as discussedabove with respect to prior figures, by varying the position of CNT 260b on feature 220, by varying height 723 of feature 220, by varyingheight 733 of feature 230, by varying height 743 of substrate material620, etc.) may be varied to further control field emissioncharacteristics. Further, it should be appreciated that one or morecomponents, objects, etc. (e.g., an alignment component for aligning theextractor and electron source, an interface component for furtheradjusting the geometry and/or configuration of electron gun 800, etc.)may be disposed between extractor 660 and 270 in other embodiments.

FIG. 9 shows exemplary array 900 of electron guns in accordance with oneembodiment of the present invention. As shown in FIG. 9, electron guns800 a-800 c are arranged on substrate 910. In one embodiment, electronguns 800 a-800 c may be coupled to substrate 910. Alternatively,electron guns 800 a-800 c may be formed from a common substrate (e.g.,910).

In one embodiment, at least one CNT electrode (e.g., comprising orcoupled to conductive material 250 a-250 c) of electron guns 800 a-800 cmay be coupled together to provide field emission current from a sharedelectric potential applied to the coupled electrodes. Similarly, atleast one extractor electrode (e.g., comprising or coupled to conductivematerial 640 a-640 c) of electron guns 800 a-800 c may be coupledtogether to provide field emission current from a shared electricpotential applied to the coupled electrodes.

In other embodiments, electron guns 800 a-800 c may be controlledindependent of one another. For example, separate electric potentialsmay be applied to one or more of the electron guns (e.g., 800 a, 800 b,800 c, etc.), where the separate electric potentials may be appliedsimultaneously and/or sequentially. In one embodiment, the separateelectric potentials may comprise different magnitudes.

Although FIG. 9 shows only three electron guns (e.g., 800 a-800 c) inarray 900, it should be appreciated that array 900 may comprise agreater or smaller number of electron guns in other embodiments.Additionally, it should be appreciated that the electrons guns of array900 may be arranged in a one-dimensional array, two-dimensional arrayand/or a three-dimensional array in other embodiments. Further, itshould be appreciated that one or more electron guns of array 900 maycomprise different characteristics, operating parameters,configurations, etc. in other embodiments.

FIG. 10 shows exemplary process 1000 for providing field emissioncurrent using an electron gun in accordance with one embodiment of thepresent invention. FIG. 11 shows exemplary field emission from exemplaryelectron gun 800 in accordance with one embodiment of the presentinvention. In one embodiment, electron gun 800 as depicted in FIG. 11(and also depicted in FIG. 8) may be used for providing field emissioncurrent in accordance with process 1000. As such, FIG. 11 will bedescribed in conjunction with FIG. 10.

As shown in FIG. 10, step 1010 involves applying an electric potentialbetween an electron source comprising a CNT and an extractor of anelectron gun. As shown in FIG. 11, electric potential 1110 may beapplied between an extractor electrode (e.g., conductive material 640)and a CNT electrode (e.g., 250) of electron gun 800. In one embodiment,electric potential 1110 may range from approximately 10 volts tohundreds of volts Extractor 660 may be mated to electron source 270(comprising CNT 260 b) to form electron gun 800. The extractor (e.g.,660) and electron source (e.g., 270) may be mated directly as depictedin FIG. 11, or alternatively, may have at least one other componentdisposed between the two (e.g., an alignment component for aligning theextractor and electron source, an interface component for furtheradjusting the geometry and/or configuration of electron gun 800, etc.).

After the electric potential is applied to the electron gun (e.g., 800),electrons may be extracted and accelerated from the CNT using theextractor to provide the field emission current in step 1020. As shownin FIG. 11, electric potential 1110 applied between CNT 260 b (e.g.,coupled to the CNT electrode formed by conductive material 250) and theconductive material (e.g., 640) of the extractor (e.g., 660) may causeCNT 260 b to emit electrons 1120 which may then be accelerated fromelectron gun 800 through aperture 810 (e.g., in the direction indicatedby arrow 1130).

As discussed above, the characteristics of the field emission currentprovided by electron gun 800 may depend on the characteristics ofelectron source 270, extractor 660, the configuration or geometry of theelectron source with respect to the extractor, or a combination thereof.As such, the field emission characteristics of electron gun 800 may beconveniently and effectively controlled by varying characteristics ofelectron source 270 (e.g. the aspect ratio of CNT 260 b). Alternatively,characteristics of extractor 660 (e.g., the location, size, shape, etc.of aperture 810) may be varied to change the field emissioncharacteristics of electron gun 800. And in other embodiments, theconfiguration or geometry (e.g., the distance between the CNT tip andthe extractor, etc.) of the electron source with respect to theextractor may be varied to change the field emission characteristics.

As shown in FIG. 11, step 1130 involves using the field emission currentto perform one or more tasks. In one embodiment, electron gun 800 may beused in electron microscopy. Alternatively, field emission current fromelectron gun 800 may be used in applications such as electron-beammetrology or electron-beam lithography (e.g., with an array of electronguns providing relatively high throughput).

In the foregoing specification, embodiments of the invention have beendescribed with reference to numerous specific details that may vary fromimplementation to implementation. Thus, the sole and exclusive indicatorof what is, and is intended by the applicant to be, the invention is theset of claims that issue from this application, in the specific form inwhich such claims issue, including any subsequent correction. Hence, nolimitation, element, property, feature, advantage, or attribute that isnot expressly recited in a claim should limit the scope of such claim inany way. Accordingly, the specification and drawings are to be regardedin an illustrative rather than a restrictive sense.

1. An electron source comprising: a substrate; a conductive materialdisposed on said substrate; a carbon nanotube coupled to said conductivematerial; and wherein said substrate comprises at least one alignmentfeature for aligning said carbon nanotube with an extractor of anelectron gun.
 2. The electron source of claim 1, wherein said substratecomprises a feature for accepting said carbon nanotube, and wherein saidcarbon nanotube is coupled to a portion of said conductive materialdisposed on said feature.
 3. The electron source of claim 1, whereinsaid carbon nanotube is welded to said conductive material.
 4. Theelectron source of claim 1, wherein said carbon nanotube is coupled in asubstantially perpendicular orientation with respect to a base of saidsubstrate.
 5. The electron source of claim 1, wherein said substratecomprises silicon.
 6. The electron source of claim 1, wherein saidconductive material comprises at least one of nickel and a metaloperable to form a strong interface with a carbon nanotube.
 7. Theelectron source of claim 1, wherein said substrate comprises at leastone alignment feature for aligning said carbon nanotube with anextractor aperture of said electron gun.
 8. A method of producing anelectron source, said method comprising: etching a substrate to create afeature for accepting a carbon nanotube; applying a conductive materialto said substrate; and coupling said carbon nanotube to a portion ofsaid conductive material disposed on said feature.
 9. The method ofclaim 8, wherein said coupling further comprises: applying an electricpotential between said carbon nanotube and said conductive material; andwelding said carbon nanotube to said portion of said conductive materialdisposed on said feature.
 10. The method of claim 8, wherein said carbonnanotube is coupled in a substantially perpendicular orientation withrespect to a base of said non-conductive substrate.
 11. The method ofclaim 8, wherein said non-conductive substrate comprises silicon. 12.The method of claim 8, wherein said conductive material comprises atleast one of nickel and a metal operable to form a strong interface witha carbon nanotube.
 13. The method of claim 8, wherein said substratecomprises at least one alignment feature for aligning said carbonnanotube with an extractor aperture of an electron gun.
 14. The methodof claim 8 further comprising: adjusting a length of said carbonnanotube using joule heating.
 15. The method of claim 15, wherein saidadjusting said length further comprises: inducing stress in a region ofsaid carbon nanotube to increase an electrical resistance of saidregion; passing a current through said carbon nanotube to induce jouleheating at said region; and adjusting said current until said jouleheating causes said carbon nanotube to break at said region.
 16. Anelectron gun comprising: an electron source comprising a carbon nanotubeand a first conductive material electrically coupled to said carbonnanotube, wherein said electron source is operable to emit electrons inresponse to an application of an electric potential to at least one ofsaid carbon nanotube and said first conductive material; an extractorcomprising a second conductive material with an aperture, wherein saidextractor is operable to at least one of extract and accelerateelectrons emitted from said electron source in response to saidapplication of said electric potential between said second conductivematerial and at least one of said carbon nanotube and said firstconductive material; and wherein said electron source comprises a firstalignment feature and said extractor comprises a second alignmentfeature, and wherein said first and second alignment features are forsubstantially aligning said carbon nanotube with said aperture.
 17. Theelectron gun of claim 16, wherein said first and second alignmentfeatures are operable to interface with one another when said extractoris mated with said electron source.
 18. The electron gun of claim 16,wherein said first conductive material is disposed on a first substrateof said electron source, wherein said second conductive material isdisposed on a second substrate of said extractor.
 19. The electron gunof claim 18, wherein said first substrate comprises said first alignmentfeature and said second substrate comprises said second alignmentfeature.
 20. The electron gun of claim 19, wherein at least one of saidfirst and second substrates comprise silicon.
 21. The electron gun ofclaim 16, wherein said first alignment feature comprises a first angledsurface and a second angled surface, wherein said second alignmentfeature comprises a third angled surface and a fourth angled surface,wherein said first angled surface is operable to interface with saidthird angled surface when said extractor is mated with said electronsource, and wherein said second angled surface is operable to interfacewith said fourth angled surface when said extractor is mated with saidelectron source.
 22. The electron gun of claim 16, wherein said carbonnanotube is welded to said first conductive material.
 23. An array ofelectron guns comprising: a first electron gun comprising: a firstelectron source comprising a first carbon nanotube, wherein said firstelectron source is operable to emit electrons in response to anapplication of an electric potential to said carbon nanotube; a firstextractor comprising a first conductive material with a first aperturefor at least one of extracting and accelerating electrons emitted fromsaid electron source in response to said application of said electricpotential between said first conductive material and said first carbonnanotube; and wherein said first electron source and said firstextractor each comprise at least one alignment feature for substantiallyaligning said first carbon nanotube with said first aperture; and asecond electron gun located in proximity to said first electron gun,said second electron gun comprising: a second electron source comprisinga second carbon nanotube, wherein said second electron source isoperable to emit electrons in response to an application of an electricpotential to said second carbon nanotube; a second extractor comprisinga second conductive material with a second aperture for at least one ofextracting and accelerating electrons emitted from said electron sourcein response to said application of said electric potential between saidsecond conductive material and said carbon nanotube; and wherein saidsecond electron source and said second extractor each comprise at leastone alignment feature for substantially aligning said second carbonnanotube with said second aperture.
 24. The electron gun array of claim23, wherein said first and second electron guns are coupled to a commonsubstrate.
 25. The electron gun array of claim 23, wherein said firstand second electron guns are formed from a common substrate.
 26. Theelectron gun array of claim 23, wherein said first and second electronguns are operable to emit electrons in response to an application of anelectrical potential to both said first and second electron guns. 27.The electron gun array of claim 23, wherein said first and secondelectron guns are independently controllable.
 28. A method of producingan extractor for an electron gun, said method comprising: identifying areference point common to both an electron source and an extractor whensaid extractor is mated with said electron source; determining arelative position of a carbon nanotube of said electron source withrespect to said reference point; and creating an aperture in aconductive material of said extractor at said relative position withrespect to said reference point, wherein said aperture is substantiallyaligned with said carbon nanotube when said extractor is mated with saidelectron source.
 29. The method of claim 28, wherein said electronsource and said extractor each comprise at least one alignment featurefor maintaining alignment of said electron source and said extractorwhen mated, and wherein said reference point is associated with saidalignment feature.
 30. The method of claim 28, wherein said referencepoint is associated with any identifiable location where said electronsource and said extractor are in physical contact with one another. 31.The method of claim 28, wherein said determining said relative positioncomprises using a scanning electron microscope to determine saidrelative position.
 32. The method of claim 28, wherein said creatingsaid aperture comprises focused ion beam milling said conductivematerial of said extractor to generate said aperture.
 33. The method ofclaim 28 further comprising: fabricating said extractor.
 34. The methodof claim 33, wherein said fabricating said extractor comprises:disposing said conductive material on a substrate; and etching saidsubstrate to create at least one alignment feature for aligning saidextractor with said electron source.
 35. A method of providing fieldemission current using an electron gun, said method comprising: applyingan electric potential between an electron source and an extractor ofsaid electron gun, wherein said electron source and said extractor eachcomprise at least one respective alignment feature for substantiallyaligning a carbon nanotube of said electron source with an aperture ofsaid extractor; and extracting electrons from said carbon nanotube usingsaid extractor to provide said field emission current.
 36. The method ofclaim 35, wherein said respective alignment features of said extractorand said electron source interface when said extractor is mated withsaid electron source.
 37. The method of claim 35, wherein said electronspass through said aperture of said extractor.
 38. The method of claim 35further comprising: accelerating said electrons through said apertureusing said extractor.
 39. The method of claim 35, wherein said electronsource further comprises a first conductive material disposed on asubstrate, and wherein said first conductive material is coupled to saidcarbon nanotube.
 40. The method of claim 39, wherein said electricpotential is applied between a second conductive material of saidextractor and at least one of said first conductive material and saidcarbon nanotube of said electron source, wherein said second conductivematerial comprises said aperture.
 41. The method of claim 35 furthercomprising: using said field emission current to perform at least one ofelectron microscopy, electron-beam metrology, and electron-beamlithography.